In the past, magnetic disk drives have been used as external storage devices to be included in workstations or servers. Along with the prevalence of personal computers or the adaptation thereof to home digital equipment, the trend toward a large storage capacity and a low cost has been encouraged. For inspection of magnetic disks or magnetic heads included in the magnetic disk drive, a method of recording or reproducing test data at an actually adopted frequency so as to assess and inspect magnetic disks or magnetic heads has been adopted. In order to reduce the cost of manufacture for the magnetic disks or magnetic heads, an inspecting apparatus for inspecting the magnetic disks or magnetic heads to be included in the magnetic disk drive (hereinafter simply called a magnetic characteristic inspecting apparatus) is requested to be compact and low-cost.
The magnetic characteristic inspecting apparatus makes it possible to mount two magnetic heads on one magnetic disk that is conventionally attached to one disk rotating device. Thus, for inspection of the magnetic head, a larger number of magnetic heads is simultaneously measurable. For inspection of the magnetic disk, the inner and outer circumferential parts of the magnetic disk are measured simultaneously. Thus, whichever of the magnetic disk and magnetic head is inspected, the throughput of testing is improved. Arts relevant to the magnetic characteristic inspecting apparatus in which two magnetic heads can be mounted include, for example, an art disclosed in U.S. Pat. No. 5,812,560 (Corresponding to Japanese Patent Laid-Open No. H10 (1998)-83501).
Assuming that the magnetic characteristic inspecting apparatus is used to inspect the characteristics of a magnetic head, the inspecting apparatus has two magnetic heads, which are objects of inspection, placed on any track of one magnetic disk which is a non-defective article or whose magnetic characteristics are already known, and records or reproduces a test signal. The characteristics of a reproduced signal are measured and assessed using measurement resources, whereby each of the magnetic heads is inspected. After the inspection is completed, the disk is stopped and the magnetic heads are replaced with uninspected articles. After the replacement is completed, the foregoing inspection is repeated.
FIG. 13 is an example of a timing chart indicating timings of inspecting two magnetic heads (magnetic heads 130 and 131) using four kinds of measurement resources (1 to 4) included in the magnetic characteristic inspecting apparatus. First, a control unit initiates an inspection A (using the measurement resource 1) of the two magnetic heads 130 and 131 at a timing t1, and transmits arbitrary frequency pattern designation data and an output enabling signal, which are needed for the inspection A, to a write signal production unit. In response to the signal, the write signal production unit transmits an arbitrary frequency pattern to a write amplifier. The magnetic heads 130 and 131 receive the signal exhibiting the arbitrary frequency pattern and record (write) the signal on respective tracks on the magnetic disk that are separated from each other by any number of tracks. At a timing t2, the magnetic heads 130 and 131 reproduce a signal from the magnetic disk, and transfer it to the measurement resources 1a, 1b, 2a, 2b, 4a, and 4b. Concurrently, the control unit transmits an enabling signal to the measurement resources 1a and 1b, and the measurement resources 1a and 1b in turn measure the respective reproduced signals or assess (measure) the characteristics of the signals.
Likewise, an inspection B (using the measurement resource 1), an inspection C (using the measurement resource 2), an inspection D (using the measurement resource 4), and an inspection E (using the measurement resource 3) are sequentially carried out. Items of characteristics to be inspected include, for example, a Track Average Amplitude (TAA) of a reproduced signal, a Pulse Width (PW), and a degree of overwriting acceptability. Frequencies at which two magnetic heads record a pattern on a magnetic disk by during each inspection may be different from each other so that recording densities in tracks immediately below the respective magnetic heads will remain constant, or may be identical to each other.
Moreover, assuming that an object of inspection is a magnetic disk, a magnetic head which is a non-defective article or whose recording or reproducing property is already known is used to inspect the magnetic disk.
By the way, U.S. Pat. No. 6,407,544 (Corresponding to Japanese Patent Laid-Open No. 2061-52319) has disclosed a magnetic characteristic inspecting apparatus in which four magnetic head holders are used to simultaneously inspect two magnetic heads placed on one magnetic disk attached to one disk rotating device, and the two magnetic heads are replaced with the other two magnetic heads so that the inspection can be uninterruptedly performed.